1. Technical Field
The present disclosure relates to methods for making cathode active materials of lithium ion batteries, and particularly to a method for making lithium iron phosphates.
2. Description of Related Art
Lithium iron phosphate (LiFePO4) is an attractive cathode active material used in lithium ion batteries. Lithium iron phosphate has the advantages of high safety, low cost, and environmental friendliness. However, lithium iron phosphate has low electronic conductivity and a slow diffusion of lithium ions, which reduce a discharge capacity of the lithium ion battery after a number of cycles. Efforts on improving the cycling performance of the lithium ion battery using the lithium iron phosphate commonly relates to improve the electronic conductivity of the lithium iron phosphate, which have been made by carbon coating the lithium iron phosphate particle surface, and doping the lithium iron phosphate with metal ions.
Solid phase method, coprecipitation method, hydrothermal method, and solvothermal method are commonly used methods for preparing lithium iron phosphate. However, the solid phase method needs a high temperature to form the product, which has a high impurity and an uncontrolled morphology. In the coprecipitation method, a precursor of the lithium iron phosphate is coprecipitated. The precursor has a low purity and low crystallization degree, thus needs further heating at a high temperature. Hydrothermal method and solvothermal method use sealed autoclave as a reactor, water or organic solvent as a reacting medium. By heating the sealed autoclave, an environment of a high temperature and high pressure is created therein, to dissolve and re-crystal an insoluble material. The hydrothermal method and solvothermal method can synthesis a product with high crystallization degree at a relatively low temperature, in short time and low energy consumption.
However, the discharge capacities of the lithium iron phosphates formed by the above described methods are still relatively low.
Therefore, what is needed is to provide a method for making lithium iron phosphate having a relatively high discharge capacity.